This invention relates to a rotor of synchronous machines, and in particular to a reinforcement of the rotor against the centrifugal force generated in synchronous machines rotating at high speed.
The rotor core of a synchronous machine is comprised of a multiplicity of laminations of blanked iron sheets. In many cases, the blanked iron sheets have as many segments and bridging sections connecting the segments as the poles. Between adjacent segments, slits extending from a point near the inner periphery to a point near the outer periphery are provided, so that the magnetic reluctance between adjacent segments is made larger than that between the rotor core and the stator core. In other words, the slits are provided for the purpose of minimizing the leakage magnetic fluxes within the rotor core. The bridging sections are provided in order to facilitate the assembly of segments, which would be difficult in the absence of the bridging sections on the one hand, and to absorb the centrifugal force while the machine is in operation on the other hand. The bridging sections, however, are required to be easily magnetically saturated and therefore are limited in width. Thus the mere provision of the bridging sections is not sufficient if the segments are to remain coupled strongly to each other against the centrifugal force.
As a measure against the centrifugal force, the method disclosed in Japanese Patent Kokai (Laid-Open) No. 3170/71 is well known. According to such a method, a clamp of non-magnetic material is provided over different segments on the outer periphery of the rotor, and both ends of the clamp, together with damper windings, are inserted fixedly into the slots, thereby coupling the segments to each other securely. In this configuration, the clamp has a uniform thickness and the ends thereof are only bonded between the slot and the damper winding. Further, in view of the difference in the coefficient of thermal expansion between the rotor core material and the damper winding material, a temperature change may cause a gap between the slot and the damper winding. The resulting disadvantage is a reduced ability of the clamp to couple the segments, thereby leading to a lower resistance to the centrifugal force. The undesirable gap between the slot and the damper winding inevitably develops especially due to the fact that the temperature of the rotor in operation is about 100.degree. C. higher than that of the rotor in stationary state. If a clamp with high rigidity is used, the clamp with the ends thereof bent at right angles and inserted into the slots is capable of enduring a considerable centrifugal force. However, a higher rigidity requires a considerably large thickness of the clamp.
If the thickness of the clamp is increased, the space between the stator core and the rotor core is required to be enlarged accordingly. As a result, the machine portion with the clamp has an increased magnetic reluctance, so that when the machine is operated as a motor, the AC magnetic field in acceleration cannot enter the rotor easily at the clamp. Thus a greater starting current is required and the accelerating torque is reduced. Furthermore, when the machine is operated as a generator, the output voltage contains more high harmonics. In order to minimize these disadvantages, the thickness of the clamp is limited, resulting in an unsatisfactory measure against the centrifugal force.